Coil springs have been used for decades to provide moment and torque protection between components. A coil spring interconnecting two components thus allows bending (moment) and torsional loads placed on a first component to be reduced and safely transmitted to the interconnected second component, thereby reducing the likelihood of a structural failure of the connection. A coil spring practically does not dissipate much of the input energy, but rather stores the input energy within the spring. If the input load is slowly built up then quickly eliminated, the released stored energy may be damaged by the quick release of the slowly input load.
U.S. Pat. No. 5,213,436 discloses a spring joint for pivotally connecting two members. A flexible torsion rod of the type generally disclosed in U.S. Pat. No. 3,118,660 is employed. A stop limits movement of the torsional rod to prevent the elastic range of the rod from being exceeded.
U.S. Pat. No. 3,118,660 discloses a torsional spring useful as a vehicular shock absorber. The device converts linearly reciprocating motion to torsional motion. The device includes an elastic torsion shaft and a pair of cam tracks on end faces of cylindrical members for imparting a twisting motion on the torsion shaft. The device is intended to limit reciprocating motion between components, and is not suitable for limiting bending and torsional loads.
U.S. Pat. No. 3,383,883 discloses a flexible coupling including axially displaceable crown gears. The flexible coupling reduces shocks and vibrations between shafts, but does not dissipate energy to provide torsional or pivotable overload protection.
An inertial stop designed to limit sudden movement between components is disclosed in U.S. Pat. No. 4,669,584. In one embodiment, the device is intended to allow limited slow rotation of one component relative to another, but is designed to limit sudden rotation between components. The device relies upon the inertia of the block, and does not limit bending and torsional loads between components.
U.S. Pat. No. 4,741,642 discloses a safety joint for a robotic arm. Linear and rotational motion between joint components is obtained by the combination of a spring acting against the weight of member 30, while a bell rod socket arrangement limits rotational motion between joint components. A breakaway action allows the release of joint components in response to excessive forces. U.S. Pat. No. 5,086,901 discloses a more elaborate overload detection device for a robotic arm. A coil spring maintains a driving member and a driven member with mutual alignment. A trip-point switch is designed to provide overload detection, but the device does not provide a force dissipating mechanism for absorbing a portion of the input moment or torque.
Many of the devices disclosed in the prior art are complex, and cannot practically be used for various applications to limit loads between components to a predetermined safe level. More particularly, prior art devices do not dissipate a significant portion of the bending and torsional energy input from one component, and accordingly significant energy is present when components return to their original configuration once the load is removed.
The disadvantages of the prior art are overcome by the present invention, and improved equipments and techniques are hereinafter disclosed for reliably limiting both bending and torsional loads between components. The device of the present invention utilizes a spring strut structure to dissipate excessive input forces. The spring strut structure automatically returns the components to their original configuration with a low energy once the excessive load is removed.